By continuing our cytogenetic and epidemiolgic survey of spontaneous abortions and their parents we will determine (1) the parental origin of trisomies, triploids and structural rearrangements; (2) the contribution of parental mosaicism to repeated abortions; (3) the correlation between mitotic and meiotic aneuploidy; (4) the effect of parental age, socio-economic status, ABO blood group incompatibility and aspects of maternal health on the etiology of both chromosomally normal and abnormal spontaneous abortions; (5) the utility of reproductive history in predicting the outcome of future pregnancies, specifically in identifying couples at risk of having trisomic conceptions and we will (6) monitor the population for exposure to any mutagens or teratogens associated with altered patterns of fetal wastage. These studies are all directed at understanding the etiology of chromosome aberrations, one of the most important causes of pregnancy wastage and mental and physical abnormalities in our species. By continuing our studies of mentally retarded individuals and their families we will determine (7) the incidence of the mar(X) syndrome in an unselected population of mentally retarded children in Hawaii; (8) the genetics of the mar(X) syndrome with special reference to mutation rate, segregation pattern, relationship of the mar(X) to age and mental retardation and the relationship between late and early replicating mar(X) chromosomes and mental impairment in heterozygotes and (9) the narute of the cytogenetic marker. We will also (10) establish norms for testicular size for Caucasian and Japanese males in the Hawaiian population and determine the contribution of Y-linked genes to any observed differences. These studies are designed to further our understanding of the mar(X) syndrome, an important cause of mental retardation in both males and females and one which is associated with a unique, but little understood, cytogenetic aberration